What do The Godfather Part III, Alien III, Spider-Man III, Terminator III, Jurassic Park III, and The Matrix Revolutions (fooled you with that last one) have in common? Well, it’s not just an affinity for a particular Roman numeral, but the fact that they represent distinctly inferior third installments to popular film trilogies. Now, we can add to that collection How to Train Your Dragon: The Hidden World, the final act to a surprisingly popular film franchise. This film isn’t a disaster, but it proves something I wouldn’t have thought possible before I saw it: this series actually ran out of gas when Gerard Butler’s character died in the previous installment.

For those unfamiliar with the storyline (and it has been five years since the last Dragon movie, another problem that the film can’t overcome), the How to Train Your Dragon films, based on a popular children’s book series by Cressida Cowell, are set some 1,000 years ago in Viking times. In the first film, the village of Berk is beset by all sorts of dragons, until the chief’s son Hiccup (voiced by Jay Baruchel) shows the villagers and his father that the two species can live together in peace. That’s how things stand as Hidden World opens. Not only do humans and dragons peacefully co-exist, but Hiccup and his dragon steed Toothless (an extremely rare type of creature called a Night Fury) lead the villagers on raids to rescue other dragons from less forward-thinking Vikings, and Berk is rapidly becoming an overcrowded animal sanctuary.

Two new characters enter the picture in Hidden World. The first is Grimmel (F. Murray Abraham), a dragon killer who allies himself with various of Berk’s human enemies who are upset that Hiccup has put a crimp in their dragon catching. The second is a female Night Fury, the first that any of the villagers or Toothless have ever seen. Naturally, Toothless falls head over heels for what Hiccup’s girlfriend Astrid (America Ferrara) dubs the Light Fury, and the two engage in some family animation, PG-level smooching and carrying on.

Soon, Grimmel launches an attack on Berk, with the aid of some acid-spitting dragons he has brainwashed to do his bidding. Hiccup and the villagers repel the attack, but they realize that Grimmel will come after them. He then remembers his late father Stoick (Butler) telling him about a “hidden world” at the edge of the ocean where the dragons came from initially. Hiccup and the Berkans set off for the hidden world in the hopes they can relocate there and live with their dragons in peace. Before they can all arrive, however, Grimmel manages to capture Toothless and plans to brainwash the Night Fury into doing his bidding as well. And, because Toothless is now the Alpha dragon, all the other beasts currently living in Berk will follow him straight to Grimmel and his trapper cohorts.

The first How to Train Your Dragon movie did a lot of things right, beginning with some terrific creature animation that turned the various species of dragons into distinct personas. This was a large part of the attraction of the author’s books originally, and the DreamWorks team headed by Dean DeBlois, who has directed all three Dragon film capture that same feel. That dazzling CGI animation is still present, but Hidden World represents yet another example of the law of diminishing returns. Simply put, we’ve seen all this before. The only thing that’s been added is the presence of the Light Fury, and she’s just a white-colored version of Toothless. Their courtship ritual is cute (and some of the best material in the movie), but a little of that goes a long way. Eventually, DeBlois goes back to flying and combat action, much of which becomes very repetitive.

The other main asset that the first Dragon movie had was the father/son relationship between Stoick and Hiccup. It’s a variant on the familiar theme of the father wanting the son to be just like him and having to overcome disappointment when that proves not to be the case. Surprisingly, the formula worked, thanks to one of Gerard Butler’s best performances. The second movie carried the formula further and added the formidable presence of Cate Blanchett as Stoick’s ex-wife. These elements managed to keep the film going even as the humor became somewhat stale.

Now, however, Butler is gone, and Blanchett is relegated to near-bit-player status. Hiccup is now an adult and the chief, and his former sidekicks, voiced by some formidable vocal talent, including Jonah Hill and Kristen Wiig, trot out the same shtick they did in the first two movies. Of course, what was funny once when done by teenagers (or actors voicing animated teenagers) isn’t nearly as amusing when done for the third time without any new material. These sidekicks grew so annoying that when Wiig’s character, Ruffnut, is captured by Grimmel, I was actively hoping she would be tortured in a way that would make the creators of the History Channel series, Vikings, proud. (Actually what happens to Ruffnut is one of the more amusing moments in Hidden World.)

The weakest aspect of How to Train Your Dragon: The Hidden World is the plot. This franchise had about one-and-a-half films worth of storyline that’s now been stretched out into three movies. Having exhausted nearly all the storylines involving the Vikings themselves other than some standard comic buffoonery, DeBlois (who also wrote the screenplay) is reduced to a weak human love story and yet another cookie-cutter villain. F. Murray Abraham can always be counted on to deliver a suitably sinister vocal performance, but Grimmel is about as generic a bad guy as there is and, worse, very similar to the big bad in the last Dragon movie.

If you distill all that works in Hidden World down to the essentials, you get a few minutes of a sweet love story between two cutesy looking dragons, the male suitably klutzy in his romantic overtures to the female. In other words, DreamWorks could, and probably should, have turned this into a short cartoon to be shown before another animated movie. I can’t argue with the success this film has had at the box office, indicating that audiences were ready for another go around with Hiccup and his dragons. However, Butler is gone, Blanchett is virtually gone, and, more important, the magic is gone. It’s not just Toothless who should be in the hidden world; this entire movie should have gone there with him.

In this clip, Hiccup and Toothless battle Grimmel and his evil dragons.